Illumination aperture filter design using superposition

Abstract

A design method, based on the principle of superposition, is presented for complex apertures used to form a filter for condenser lens illumination in an optical reduction system. The method is relatively simple to implement and achieves near optimum results without the need to perform long and error prone calculations. Both OPE and DOF are simultaneously optimized over a wide range of duty ratios.

What is claimed is:  
     
       1. A method of illumination aperture filter design, comprising: 
       generating, through simulation, a first illumination aperture filter design that is optimized only for depth of focus;  
       generating, through simulation, a second illumination aperture filter design that is optimized only for proximity effects; and  
       superimposing the first design on the second design, thereby generating a third illumination aperture filter design that is optimized for both depth of focus and proximity effects.  
     
     
       2. The method of  claim 1  wherein said third illumination aperture filter design is effective over a duty ratio that is about 1:N, where N≧1. 
     
     
       3. The method of  claim 1  wherein said third illumination aperture filter design has four identical quadrants and is effective for illuminating wavelengths between about 90 and 365 nm. 
     
     
       4. The method of  claim 1  further comprising generating said first and second designs by combining square and circular apertures. 
     
     
       5. A method of illumination aperture filter design, comprising: 
       generating, through simulation, a first illumination aperture filter design that is optimized only for depth of focus;  
       generating, through experimentation, a second illumination aperture filter design that is optimized only for proximity effects; and  
       superimposing the first design on the second design, thereby generating a third illumination aperture filter design that is optimized for both depth of focus and proximity effects.  
     
     
       6. The method of  claim 5  wherein said third illumination aperture filter design is effective over a duty ratio that is about 1:N, where N≧1. 
     
     
       7. The method of  claim 5  wherein said third illumination aperture filter design has four identical quadrants and is effective for illuminating wavelengths between about 90 and 365 nm. 
     
     
       8. The method of  claim 5  further comprising generating said first and second designs by combining square and circular apertures. 
     
     
       9. A method of illumination aperture filter design, comprising: 
       generating, through experimentation, a first illumination aperture filter design that is optimized only for depth of focus;  
       generating, through simulation, a second illumination aperture filter design that is optimized only for proximity effects; and  
       superimposing the first design on the second design, thereby generating a third illumination aperture filter design that is optimized for both depth of focus and proximity effects.  
     
     
       10. The method of  claim 9  wherein said third illumination aperture filter design is effective over a duty ratio that is about 1:N, where N≧1. 
     
     
       11. The method of  claim 9  wherein said third illumination aperture filter design has four identical quadrants and is effective for illuminating wavelengths between about 90 and 365 nm. 
     
     
       12. The method of  claim 9  further comprising generating said first and second designs by combining square and circular apertures. 
     
     
       13. A method of illumination aperture filter design, comprising: 
       generating, through experimentation, a first illumination aperture filter design that is optimized only for depth of focus;  
       generating, through experimentation, a second illumination aperture filter design that is optimized only for proximity effects; and  
       superimposing the first design on the second design, thereby generating a third illumination aperture filter design that is optimized for both depth of focus and proximity effects.  
     
     
       14. The method of  claim 13  wherein said third illumination aperture filter design is effective over a duty ratio that is about 1:N, where N≧1. 
     
     
       15. The method of  claim 13  wherein said third illumination aperture filter design has four identical quadrants and is effective for illuminating wavelengths between about 90 and 365 nm. 
     
     
       16. The method of  claim 13  further comprising generating said first and second designs by combining square and circular apertures. 
     
     
       17. An illumination aperture filter, comprising: 
       a first part, that is optimized only for depth of focus; and  
       a second part optimized only for proximity effects.  
     
     
       18. The illumination filter described in  claim 17  wherein said first part further comprises an assemblage of square and circular apertures. 
     
     
       19. The illumination filter described in  claim 17  wherein said second part further comprises an assemblage of square and circular apertures. 
     
     
       20. The illumination filter described in  claim 17  wherein the filter has a diameter between about 1 and 50 cm and further comprises four identical quadrants.